ABCA3 and the Pathogenesis of Acute and Chronic Lung Disease - This grant application is designed to test the hypotheses that (1) ABCA3 transport protein plays a complex and critical role in alveolar homeostasis, and (2) mutations and deficits in ABCA3 function cause and modify acute and chronic lung disease in infants and adults. The application is based on preliminary data demonstrating that mutations in the human ABCA3 gene cause severe lung disease which varies in time of presentation and severity. In this grant application, we will determine the role of the mouse Abca3 gene in alveolar homeostasis, generating and utilizing mice in which the Abca3 gene has been conditionally deleted in respiratory epithelial cells, creating null or partial deletions of the gene. The molecular and cellular consequences of Abca3 deletion, deficiency, and mutation will be determined in vivo and in vitro. We will assess whether cell-specific effects of selected ABCA3 mutant proteins (associated with human disease) alter routing, stability, and function of the protein. In vivo and in vitro studies will assess whether altered synthesis, routing, and function of the mutant protein cause cell injury that might contribute to the pathogenesis of lung disease. Genes modifying the disorder will be identified in transgenic mice and in cell lines using mRNA microarray analyses. Strain-dependent differences in the severity of lung disease will be assessed after breeding of the Abca3 mutant mice into susceptible and non-susceptible strains of mice. Susceptibility of Abca3 mutant mice to secondary injury by oxygen and endotoxin will be determined in vivo. Expression of the Abca3 gene will be studied at transcriptional and post-transcriptional levels to determine the mechanisms controlling ABCA3 expression. Immunocytochemistry and lung morphology will be correlated with ABCA3 mutations in human tissues. We will test the hypothesis that susceptibility to lung disease at birth, and thereafter, may be influenced by the levels of ABCA3. We will determine the levels of expression of ABCA3 during development and after lung injury in mice. Immunological, biochemical, and structural markers of ABCA3 dysfunction will be sought to enhance our ability to diagnose ABCA3-related lung disease. Long-term goals of this application seek to understand the role of ABCA3 in the pathogenesis of both inherited and acquired lung disease, to identify genes (pathways) modifying disease pathogenesis, and to develop new strategies to enhance ABCA3 function for the treatment of acute and chronic lung disease in humans.